1. Technical Field
The present invention relates to a differential signal transmission apparatus and a test apparatus using the differential signal transmission apparatus. In particular, the present invention relates to a differential signal transmission apparatus that transmits a differential signal and a test apparatus that uses the differential signal transmission apparatus.
2. Related Art
A test apparatus having a test head with multi-channel pin electronics circuit and a performance board that inputs a test signal generated by the pin electronics circuit into a device under test is known as in, for example, International Publication Pamphlet No. 2004/090561. A signal output apparatus that outputs a differential signal as the test signal to be input to the device under test is known to be used by the above test apparatus as in, for example, Japanese Patent Application Publication No. 2000-009804.
In the test apparatus described above, each multi-channel pin electronics circuit is connected to the performance board by a plurality of transmission lines. The plurality of transmission lines transmit test signals generated by the pin electronics circuit to the performance board. In order to decrease the noise in the transmission lines, the test apparatus includes positive signal transmission lines for transmitting positive signals and negative signal transmission lines for transmitting negative signals. In order to test a variety of semiconductor devices, the plurality of transmission lines are preferably able to send a single end signal in addition to the differential signal. In this case, the positive signal transmission line and the negative signal transmission line are both coaxial cables, and the positive signal and the negative signal are sent on the respective coaxial cables when transmitting the differential signal.
In the test apparatus described above, however, a difference in the length between the positive signal transmission line and the negative signal transmission line or a difference in characteristics of the electrical elements arranged on the positive signal transmission line and the negative signal transmission line causes a skew between the negative signal and the positive signal transmitted thereon. If the positive signal and the negative signal making up the differential signal are each transmitted on independent coaxial cables, the skew is very likely to occur between the signals because there is often a difference between the lengths of the transmission paths in the coaxial cable transmitting the positive signal and the coaxial cable transmitting the negative signal. This skew can cause an operational error in the semiconductor device being tested, which makes it difficult to accurately measure the signal output from the semiconductor device as a test result.